The invention relates to a method for controlling the reel structure, in which method a continuous paper web is reeled around a reel spool to form a reel, and one or several variables are measured from the web. The invention also relates to an apparatus for controlling the structure of the reel. The reeling in question is a continuous reeling up in which successive machine reels are formed from a paper web passed into the reel-up at the running speed (web speed).
In the terminal end of the paper or paperboard machine or in a finishing apparatus, such as a coating machine, a continuous fibrous web passed from the preceding sections is reeled around a rotating reeling shaft (i.e. a reel spool) to form a reel, a so-called machine reel. The reeling is conducted by means of a reeling cylinder rotating at web speed, via which the web is passed on the reel. A loading is maintained between the reeling cylinder and the reel, which loading causes a particular nip load in a reeling nip located in the contact point of the reel and the reeling cylinder approximately in parallel relationship with the reeling shaft. The loading is typically implemented by loading the reel by means of a loading mechanism coupled to the ends of the reeling shaft, towards a reeling cylinder located in a fixed position in the frame of the reel-up at the same time when the reeling shaft, supported at its ends, moves further away from the reeling cylinder along with the growth of the reel. For the above-described reel-up type, the term Pope reel-up is used. In these reel-ups, it is possible to implement the rotation of the reeling shaft and the reel by means of a surface draw, wherein the reeling shaft rotates freely in the supporting structures of the reel-up, and the force required for rotation is transmitted from the reeling cylinder to the reel via the reeling nip, or by means of a centre-drive, wherein not only the reeling cylinder but also the reeling shaft is provided with a drive.
The reel-up type functioning by means of a surface draw is disclosed for example in the Finnish patent 71107 and in the corresponding U.S. Pat. No. 4,634,068. A centre-drive assisted reel-up is presented for example in the Finnish patent application 905284 and in the corresponding U.S. Pat. No. 5,251,835. A centre-drive assisted reel-up with a separate loading mechanism is disclosed in the European patent 604558 and in the corresponding U.S. Pat. No. 5,393,008.
Because continuous web is passed from the preceding sections of a paper or paperboard machine or from the finishing apparatus for the web at the running speed of the machine or apparatus, it is necessary to conduct a reel change at intervals, i.e., when the reel becomes full in the reeling station, the web is cut in a suitable manner, dependent e.g. on the grammage of the web, and the new end of the web following the cut-off point is guided around a new empty reeling shaft, which has been brought in the change station earlier from a storage of reeling shafts, i.e. a reel spool storage. There are a number of patents and patent applications related to this change sequence or a part of it, and herein it is possible to mention the Finnish patent 95683 and the corresponding international publication WO 93/34495 (member pressing the web and preventing access of air into the reel) as well as the Finnish application 915432 and the corresponding U.S. Pat. No. 5,360,179 (cutting of a web by means of a water jet) and the Finnish patent 97339 and the corresponding European application publication 739695 (striking blade cutting device for cutting of a web with a full-width cut).
The reeling cylinder typically has a fixed position in the frame of the reel-up. However, there is also a known reel-up solution, in which the reeling cylinder is arranged in the frame to move in the vertical direction and to be loaded against the reel whose position on the reeling rails is arranged adjustable. The solution, which is presented in the European patent 697006 makes it possible to move the reeling shafts along a straight path from the storage of reel spools on the reeling rails over the top of the reeling cylinder, and enables a fixed position of the reeling shaft during the reeling by compensating the growth of the reel with a downward motion of the reeling cylinder. The European application publication 792829 discloses a reel in which the reeling cylinder to be loaded against the reel is able to move in the horizontal direction when the size of the reel grows and the reeling shaft rotates in its position.
Consequently, there are a number of known reel-up concepts. It is common to all aforementioned reel-up concepts that they comprise a reeling cylinder with a fixed position or a moving reeling cylinder, as well as a growing machine reel which is in nip contact with the same. A common feature to all reel-up concepts is an accurate and demanding change sequence implemented by means of an empty reeling shaft brought in contact with the same. A disturbance-free change sequence with the purpose of avoiding broke, sets high demands on the actuators and on the automation. At present, especially the high web speeds, which normally exceed 20 m/s, generally already 25 m/s, set demands for a disturbance-free function of the reel-up so that it would be possible to obtain machine reels which are as flawless as possible.
During the reeling that takes place in the reeling station itself, the aim is to affect the structure of the reel to be produced by means of the linear pressure (linear load) effective in the reeling nip. According to present-day knowledge, the reeling result of the reel-up clearly correlates with the transverse profiles of the web to be reeled. It has been observed that a particularly problematic profile is a xe2x80x9csmilingxe2x80x9d or a xe2x80x9ccup-likexe2x80x9d transverse profile of the thickness, which, on the basis of calculations, is known to cause rising edges also in the shape of radial pressure distribution graph inside the reel.
According to a theory, a web whose edges are thicker than the central part, produces forces inside the machine reel which can cause inner movements. As a result of the movements, the core of the machine reel can stick out, which causes bottom or edge cracks.
The web is passed on the reel via a reeling nip, in which nip the radius of the reel can be rendered smaller than average (the reel is compressed slightly), and thus it is possible to affect the compression of the reel in the nip, in other words the radial difference, which produces a suitable/desired tight reeling on the reel. Especially when paper is reeled which has been processed with a so-called multi-roll calender in which paper is passed via several nips and in which the linear loads are very high, even of the order of 400 kN/m, new requirements are set for the reeling. Because it is not typically possible to use linear loads which are even close to this order in the reeling, but they are approximately max. 6 kN/m, the radius of the reel does not change significantly in the reeling nip, and thus, the formation of the reel has to be conducted in a centre-drive assisted manner in association with passing of the paper on the reel via the nip, wherein the air is controlled by means of the nip, and the centre-drive is utilized to set the tension of the web on the reel.
Thus, in connection with a multi-roll calendered paper the situation is somewhat different than when reeling uncalendered paper; in the reel-up the applicable area of the linear load can be even 50 times smaller than the linear load used in the multi-nip calender. At the reel-up the web pressed once with a great force is run through a nip load which is 50 times smaller, and thus, the effect on the paper is no longer significant. Especially in this kind of a process, the variations in the thickness will become pronounced in the formation of the reel.
The transverse profiles of the web are produced by means of the paper machine and the finishing apparatuses before the reeling up process. As an example of an adjustment conducted by means of the paper machine or the finishing apparatus for paper, it is possible to mention the U.S. Pat. No. 5,649,448. It is not possible for the reel-up to affect the properties of the web, but the last point in which the properties of the paper are affected is calendering. On the other hand, by means of the reel-up, it should be possible to reel a machine reel even from a web which has a poor transverse profile, without defects or losses of material produced by the reeling. Along with the running speeds, the aim is to increase the size of the machine reels reeled in the reel-up. When the diameter of the reel grows, also the requirements for a homogenous quality of the web are increased.
It is an object of the invention to eliminate the drawbacks due to prior art reeling processes, and to introduce a method by means of which the flaws in the quality of the reels to be reeled can be reduced. To attain this purpose, the method according to the invention is primarily characterized in that when a particular, predetermined change occurs in the variable, the lateral oscillation of the web is changed, by means of which the web is guided to different locations in the reel in the axial direction of the reel spool.
It is another object of the invention to improve the reeling result by using the oscillation of the web as an active manipulated variable. When a change is detected in the measurement conducted on the web, the oscillation, by means of which the web is guided on different points of the reel in the axial direction of the reel spool, is changed. The change in the oscillation can be such that the oscillation amplitude is normally zero, i.e. it is non-existent, and the oscillation is initiated when a change is detected in the variable measured from the web in the measuring point measuring the properties of the web, which change has an impairing effect on the quality of the reel. The measurement, on the basis of which the oscillation is determined, can be the measurement of the transverse profile of the web at a suitable point in the travel path of the web by means of a suitable method. The act of starting the oscillation of the web as well as the amount of oscillation can be dependent on the quality of the transverse profiles. The invention can be implemented in such a way that when the dispersion in the measurement of thickness or another variable describing the irregularity of the transverse profile exceeds a particular threshold value, the oscillation begins. The change of the oscillation can also be performed when the oscillation is on. The quantitative adjustment of the oscillation can be implemented in such a way that when a dispersion in the on-line thickness measurement of the web or another variable correlating with the irregularity of the transverse profile grows, the amplitude and/or speed of the oscillation is increased. When taken a step further, the adjustment can also take into account the shape of the profile, wherein the amplitude and/or speed of the oscillation could be adjusted on the basis of the same.